In glycolysis, which intermediate donates a phosphate to ADP to generate ATP during substrate-level phosphorylation?

• A. 1,3-Bisphosphoglycerate
• B. 3-Phosphoglycerate
• C. Phosphoenolpyruvate
• D. Pyruvate

Answer: (A)

Substrate-level phosphorylation in glycolysis happens when a high-energy phosphate is directly transferred from an intermediate to ADP to form ATP. The classic donor in the first such step is 1,3-bisphosphoglycerate. In the glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate reaction, energy is stored in the high-energy phosphate bond, and when that phosphate is transferred to ADP, ATP is produced and the molecule becomes 3-phosphoglycerate. This is the key example students learn for how glycolysis makes ATP without using the electron transport chain.

Note that there is another substrate-level phosphorylation later in glycolysis where phosphoenolpyruvate donates its phosphate to ADP to form ATP and pyruvate. However, the specific intermediate that donates the phosphate in the well-known early SLP step is 1,3-bisphosphoglycerate, which is why it’s the best answer here. The product in that step is 3-phosphoglycerate, not a phosphate donor.